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The company said the tax break removed “a major obstacle” which had prevented the field from being fully developed.

Mr Osborne said: “Gas is the single biggest source of energy in the UK. Today the government is signalling its long-term commitment to the role it can play in delivering a stable, secure and lower-carbon energy mix.”

Centrica said it was expecting to pay the Treasury £1 billion in tax revenues from Cygnus, as well as creating 4,000 jobs.

The Government said the gas would continue to play an important part in the energy mix beyond 2030, to complement “intermittent” supply from renewable sources.

The deal was a compromise between the department – which is led by Liberal Democrat Cabinet minister Ed Davey - and Mr Osborne, who had been pushing for cuts of 25 per cent.

Mr Osborne had offered to drop his demands for deeper cuts in subsidies for onshore wind farms if the Lib Dems compromised on retaining a big role for natural gas rather than commit to the virtual de-carbonisation of the power sector by 2030.